1. Field of the Invention
The present invention relates to Faraday rotators, optical isolators, polarizers and diamond-like carbon thin films, and more particularly relates toxe2x80x94in optical communications fieldsxe2x80x94Faraday rotators for rotating light-wave polarization planes, optical isolators for blocking return beams from a light source, polarizers for transmitting only a given polarized component of light, and to diamond-like carbon thin films utilized as materials in optical communications fields.
2. Description of the Background Art
In optical communications systems constituted from optical fibers and optical elements, reflected light from optical-connector junctions and optical circuit components is sometimes reintroduced to the light source. Noise produced by beams returning to a light sourcexe2x80x94especially to a semiconductor laserxe2x80x94often turns out to be a major problem in designing optical communications systems and optical devices.
The means commonly used for blocking off the return beams is an optical whose constituent elements are a Faraday rotator, a polarizer, an analyzer, and a magnetic part.
By virtue of the magnetic part applying a magnetic field to a magneto-optical (magneto-optical material), Faraday rotators rotate the polarization plane of an incident light beam traveling in the direction of the magnetic field. Meanwhile, polarizers (analyzers) allow only a given polarized light component to pass, and block components apart from that which is polarized.
As illustrated in FIG. 14, an optical isolator 6 is configured as an assembly of a polarizer 2, a Faraday rotator 3, an analyzer 4, and a magnetic part 5, and the non-repelling characteristics of the magneto-optical material are exploited to block the incident light from being reintroduced from the opposite direction. A general optical-isolator assembly will be more specifically described in the following, while reference is made to FIG. 14.
Incident light from a light source 1 initially is filtered through the polarizer 2 into a polarization plane, and then transits the Faraday rotator 3, whereby the polarization plane is rotated 45 degrees. With its polarization plane rotated by 45 degrees the incident light passes through and radiates as it is from the analyzer 4, and in part once more enters the analyzer 4 as a return beam and is reintroduced into the Faraday rotator 3. The polarization plane of the return beam is again rotated 45 degrees by the Faraday rotator 3, and with its polarization plane having been rotated 90 degrees in total, the return beam is unable to pass through the polarizer 2, where the return beam is thus blocked off.
It will be understood that the arrows drawn at certain angles with respect to the arrows indicating either the light emitted from the light source 1 or the return beam are schematic representations of the polarization directions of either the emitted light or the return beam.
Yttrium iron garnet (YIG hereinafter) crystals or bismuth-substituted garnet crystals have usually been used for conventional Faraday rotators (magneto-optical bodies). Furthermore, for conventional polarizers (analyzers), rutile (titanium oxide) monocrystals or glass superficially onto which silver particles are orientated in a single direction are usually used, while for the magnetic part that applies a magnetic field to the magneto-optical body, samarium-based rare-earth magnetic substances are
The YIG crystals or bismuth-substituted garnet crystals chiefly used for conventional Faraday rotators must have a certain thickness to obtain a needed Faraday rotation angle, which results in a large external form. Likewise, the external form becomes large in the case of the rutile monocrystals and the glass onto which silver particles are superficially orientated in a single direction, that have been chiefly used for conventional polarizers (analyzers), and the samarium-based rare-earth magnetic substances chiefly used as the magnetic part for applying a magnetic field to the magneto-optical body, since they must occupy a certain volume. What is more, with conventional isolators especiallyxe2x80x94whose basic constituent elements are a Faraday rotator, a polarizer (analyzer) and a magnetic partxe2x80x94has been the problem of being large-sized overall.
Meanwhile, Faraday rotators, polarizers (analyzers) and magnetic bodies are expensive, making conventional optical isolators in which these are the constituent elements cost all the more. A further problem has been that because the individual constituent elements in conventional optical isolators are independent, their assembly process is complex, adding that much more to the cost.
Moreover, because as a general rule what determines a Faraday-rotator angle is thickness, conventional Faraday rotators can only correspond to a single wavelength. The consequent problem too with conventional optical isolators having a conventional Faraday rotator as a constituent element has been that they basically can handle only a single wavelength.
Given the foregoing, objects of this invention are: first, to miniaturize and hold down the cost of, respectively, Faraday rotators, polarizers, analyzers, magnetic bodies, and optical isolators in which these are the constituent elements; second, to enable a Faraday rotator and an optical isolator to handle a plurality of wavelengths; and third, a new material useful in miniaturizing and in lowering the cost and enhancing the performance of polarizers to begin with, and of various optical devices.
The invention in being a Faraday rotator having wavelengh selectivity, for selectively rotating only the polarization plane of incident light of given wavelengths, is characterized in being furnished with: a magneto-optical section that rotates the polarization plane of incident light traveling in the direction of its magnetic field; and a dielectric multi-layer film in which a low refractive-index layer and a high refractive-index layer are laminated in alternation, for localizing within the magneto-optical section incident light of at least one wavelength.
Preferably, the dielectric multi-layer film is characterized in localizing within the magneto-optical section incident light beams of plural wavelengths.
Further preferably, the magneto-optical section is characterized in being constituted from a gadolinium iron garnet thin film.
Further preferably, the dielectric multi-layer film is characterized in being composed by laminating in alternation silicon oxide as a low refractive-index layer, and titanium oxide as a high refractive index layer.
Further preferably, the magneto-optical section and the dielectric multi-layer film are characterized in being formed integrally by a vapor-phase process.
Under a separate aspect the invention in being an optical isolator having wavelength selectivity, for selectively blocking only return beams from incident light of given wavelengths, is characterized in being furnished with: a magneto-optical section for rotating the polarization plane of incident light traveling in the direction of its magnetic field; a magnetic part for applying a magnetic field to the magneto-optical section; a dielectric multi-layer film in which a low refractive-index layer and a high refrative-index layer are laminated in alternation, for localizing within the magneto-optical section incident light of at least one wavelength; a polarizer for picking out polarized components from incident beams; and an analyzer utilized in combination with the polarizer.
Preferably, the dielectric multi-layer film characterized in localizing within the magneto-optical section incident light beams of plural wavelengths.
Further preferably, the magneto-optical section is characterized in being constituted from a gadolinium iron garnet thin film.
Further preferably, the magnetic part is characterized in being constituted from a gallium nitride magnetic semiconductor thin film that exhibits ferromagnetism at room temperature and is transparent to light.
Further preferably, the dielectric multi-layer film is characterized in being composed by laminating in alternation silicon oxide as a low refractive-index layer, and titanium oxide as a high refractive index layer.
Further preferably, the polarizer and the analyzer are characterized in being lent a structure having distributed refractive indices, by irradiating with either a particle beam or an energy beam a diamond-like carbon thin film along a bias with respect to the film""s thickness direction.
Further preferably, the particle beam is characterized in being an ion beam, an electron beam, a proton beam, xcex1-rays, or a neutron beam; and the energy beam in being light rays, X-rays or xcex3-rays.
Further preferably, the magneto-optical section, the magnetic part, the dielectric multi-layer film, the polarizer, and the analyzer are characterized in being formed integrally by a vapor-phase process.
Further preferably, the polarizer and the analyzer are characterized in utilizing a diamond-like carbon thin film that is transparent in the light region, and that has an extinction coefficient that is 3xc3x9710xe2x88x924 or less at optical-communications wavelengths of from 1200 nm to 1700 nm.
Under another aspect the invention in being a polarizer is characterized in being lent a structure having distributed refractive indices, by irradiating with either a particle beam or an energy beam a diamond-like carbon thin film along a bias with respect to the film""s thickness direction.
Preferably, the particle beam is characterized in being an ion beam, an electron beam, a proton beam, xcex1-rays, or a neutron beam; and the energy beam in being light rays, X-rays or xcex3-rays.
Further preferably, the polarizer is characterized in utilizing a diamond-like carbon thin film that is transparent in the light region, and that has an extinction coefficient that is 3xc3x9710xe2x88x924 or less at optical-communications wavelengths of from 1200 nm to 1700 nm.
According to another aspect of the invention, the diamond-like carbon thin film is characterized in being transparent in the light region, and in having an extinction coefficient that is 3xc3x9710xe2x88x924 or less at optical-communications wavelengths of from 1200 nm to 1700 nm.
Further preferably, optics components are characterized in utilizing a diamond-like carbon thin film that is transparent in the light region, and whose extinction coefficient is 3xc3x9710xe2x88x924 or less at optical-communications wavelengths of from 1200 nm to 1700 nm.
Accordingly, under this invention, miniaturizing and moreover holding down the costs of Faraday rotators, polarizers, analyzers, magnetic parts, and optical isolators having these as their constituent elements, is made possible. Likewise, manufacturing Faraday rotators and optical isolators that can handle plural wavelengths is made possible. Furthermore, a new material useful in miniaturizing and in lowering the cost and enhancing the performance of polarizers to begin with, and of various sorts of optical devices, can be provided.
From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.